Short-term Investments

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Short-term Investments

3. Short-term Investments

Short-term investments consisted of available-for-sale securities as follows:

Type of security as of December 31, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(In thousands)
U.S. government-related debt securities	$	4,502	$	—	$	(4	)	$	4,498
Corporate debt securities		47,345		2		(40	)		47,307
Asset-backed securities		3,198		—		(1	)		3,197
Total available-for-sale securities	$	55,045	$	2	$	(45	)	$	55,002
Type of security as of December 31, 2013	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(In thousands)
U.S. government-related debt securities	$	1,565	$	1	$	—		$	1,566
Corporate debt securities		31,128		24		(3	)		31,149
Total available-for-sale securities	$	32,693	$	25	$	(3	)	$	32,715

The fair values of available-for-sale securities by contractual maturity at December 31 were as follows:

	2014		2013
	(In thousands)
Maturing in one year or less	$	51,235	$	26,725
Maturing in one to three years		3,767		5,990
Total available-for-sale securities	$	55,002	$	32,715

The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and none have been in a continuous unrealized loss position for more than 12 months as of December 31, 2014:

	Less Than 12 Months
	Fair value		Gross unrealized losses
	(In thousands)
U.S. government-related debt securities	$	2,996	$	(4	)
Corporate debt securities		30,372		(40	)
Asset-backed securities		2,259		(1	)
Total	$	35,627	$	(45	)

The Company invests in securities that are rated investment grade or better. The unrealized losses on investments as of December 31, 2014 were primarily caused by interest rate increases.

The Company reviews the individual securities in its portfolio to determine whether a decline in a security’s fair value below the amortized cost basis is other-than-temporary. The Company determined that as of December 31, 2014, there were no investments in its portfolio that were other-than-temporarily impaired.